Lac Des Iles Mine, Canada

The Lac Des Illes mine is an open pit and underground operation located 85km from Thunder Bay in Ontario, Canada. The mine consists of the Roby zone and the offset zone and extends over 86.4km2 of mineral claims and leases. Open pit mining began in 1993. By the second quarter of 2004 underground mining had also commenced to access the higher grade portion of the Roby Zone.

The mine is owned and operated by North American Palladium. In 2008, the company placed the mine on care and maintenance for a temporary basis as a response to plunging metal prices. Production resumed on 14 April 2010 when prices began to recover. Due to the short life of the open pit mine, the company is planning to close it and focus on the underground operations.

Reserves

The mine includes an estimated 36Mt of measured and indicated resources graded at 3.18g/t of Pd, 0.26g/t Pt, 0.22g/t Au, 0.07% Cu and 0.09% Ni.

Measured and indicated resources have been estimated by including the Roby Zone's open pit, stockpile and underground resources and the underground resources at offset.

Inferred resources, including only offset underground, stand at 4.6Mt graded at 4.9g/t Pd, 0.4g/t Pt, 0.3g/t Au, 0.12% Au,0.12% Cu and 0.13% Ni.

Geology

The mine lies within a 3km-long and 1.5km-wide oval-shaped intrusive package hosted in the southern portion of the Archean-aged Lac des Iles Intrusive Complex. Termed as the Mine Block intrusive, the rocks host several platinum-group metal deposits with the most important being the Roby Zone.

The Roby zone is further divided into three sub-zones namely the north Roby zone, Roby underground zone/high grade zone, and the breccia zone. The offset zone, created by a fault-caused displacement, is a deep extension of the Roby underground zone.

The rocks are complex in terms of texture and composition. Compositionally, the rocks vary from anorthosite to clinopyroxenite and leuco-gabbronorite to melanonorite. It includes magnetite-rich gabbro. Texturally, the rocks are either equigranular, porphyritic, fine to coarse-grained, pegmatitic, variably textured or heterolithic gabbro breccias.

Mineralisation

Mineralisation at Lac Des Iles is largely strata-bound, rarely visible and unpredictable. Massive PGE mineralisation is found within an elliptical domain that lies directly south of the lac des Iles area. A domain further southward is characterised by widespread medium-grained PGE-barren gabbronorite that contains low PGE content.

Within the elliptical domain, large amount of monolithic and heterolithic breccia with nominal content of gabbronorite is found. A large, medium-grained gabbro, East Gabbro, lies adjacent to a varitextured gabbro in the west. The varitextured gabbro hosts the Roby palladium deposit where heterolithic gabbro breccia exist as pipes, pods and massive blocks. The heterolithic gabbro breccia hosts a high grade ore that is limited within an ultramafic unit.

The East Gabbro lies beside an equigranular gabbronorite. Ore grade mineralisation is found within gabbroic to pyroxenitic rocks that are associated with disseminated or blebby secondary sulphides and characterised by immense sausseritization of plagioclase feldspars and strong alteration of talcose to amphiboles. Much of the high-grade zone is hosted along the contact between the East Gabbro and the heterolithic gabbro breccia.

Mining

The mine produces, on an average, 15,000tpd of ore from both open pit and underground operations. The open pit is mined using hydraulic 23m3 and 27m3 shovels, 187mm blast hole drills, 190t trucks and a fleet of support equipment. Mining involves 10m benches and 15m berms. The walls are angled at 57° in the east and the west, and 45° in the south.

A distance of 90m still exists between the open pit and the highest level mined underground. To reach the underground zone, a decline ramp was descended at 20m to 30m levels. Mining has been carried out using both longitudinal and transverse longhole stoping. Two hydraulic drill jumbos besides a mechanised rock bolter and two scissor lifts have been used.

To conduct the production drilling, a set of in-the-hole long hole drills has been used. Mucking is carried out using a combination of 8yd3 and 11yd3 Tamrock scoop trams that have carried a fleet of three 60t haul trucks. Ore is transported and stockpiled at the portal in the open pit from where it is sent to the crusher into 190t 730E haul trucks.

Processing

The processing plant produces bulk palladium, nickel and copper concentrate that contains high PGM credits. Flotation operation is conducted in a conventional mill with SAG and ball milling. The final product is achieved after three steps of flotation and two steps of re-grind.